We’re introducing Claude Fable 5.1 and Claude Mythos 5.1. They're the world’s most advanced models for coding and knowledge work.
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Fable 5.1 excels at complex, long-running tasks. And its research capabilities offer an early glimpse of how AI models will contribute to scientific progress.

Sep 1, 2026 · 6:03 PM UTC

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Across our benchmarks, the model sets a new standard. It scores 52.6% on Terminal-Bench-Science 0.1, more than double Fable 5. On Terminal-Bench 4.0, it scores 55.8% against 42.0% for Fable 5.
Benchmark table comparing Claude Fable 5.1 with Fable 5, Opus 5, and GPT-5.6 Sol across seven evaluations. Fable 5.1 leads on every row, including 52.6% on Terminal-Bench-Science 0.1 and 55.8% on Terminal-Bench 4.0.

ALT Benchmark table comparing Claude Fable 5.1 with Fable 5, Opus 5, and GPT-5.6 Sol across seven evaluations. Fable 5.1 leads on every row, including 52.6% on Terminal-Bench-Science 0.1 and 55.8% on Terminal-Bench 4.0.

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As well as being capable of much higher performance than Fable 5, it can also achieve similar or better results at a much lower cost when set to lower effort levels.
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Cache reads with Fable 5.1 cost 75% less than Fable 5’s. This reduces the cost of the model in practice by around 25% for typical workloads, and up to 45% for highly agentic ones.
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We’re also introducing Enterprise Frontier Safeguards (EFS), which give enterprise customers complete privacy (the same as zero data retention), while still being state-of-the-art at preventing adversarial use. EFS rolls out in phases, starting this fall. anthropic.com/news/enterpris…

Developing Enterprise Frontier Safeguards with our customers

Anthropic is an AI safety and research company that's working to build reliable, interpretable, and steerable AI systems.

anthropic.com
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Finally, we’ve improved our safeguards. Our cybersecurity safeguards now flag benign requests about 60% less often. On basic biology and medical questions, we’ve recently reduced the fallback rate by around 85%.
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Claude Fable 5.1 is available everywhere today. Claude Mythos 5.1, our model for cyberdefenders and life scientists, is available through trusted access programs. Read more: anthropic.com/claude-fable-a…

Introducing Claude Fable 5.1 and Claude Mythos 5.1

Our most advanced models for coding and knowledge work. Their research capabilities also offer an early glimpse of how AI models will contribute to scientific progress.

anthropic.com
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Sort replies: Relevant Recent Liked
Replying to @claudeai
one prompt on ultracode. excuse me?
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Replying to @claudeai
Great video @alexalbert__ ! Well done!
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Replying to @claudeai
This feels like a real step toward useful research assistance
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Replying to @claudeai
Bruh, why does Opus 5 became GPT 2.5?
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Replying to @claudeai
"Available everywhere" except Pro plan.
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Replying to @claudeai
Made with AI
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Replying to @claudeai
I took that MAX subscription for fable for few months to build an applocation but just yesterday unsubscribed claude, its stupid and breaks code to introduce new bugs . Not consistent. Also. tokens are used by it carelessly . It doesnt honour our money and effort.I had recharge another 800$ just to fix bugs it introduced
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Replying to @claudeai
It’s unusable after 5 questions it uses up all session usage. Trash!
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Replying to @claudeai
I just canceled my pro subscription. If I can't access the latest model, I see no point in giving my money to Anthropic.
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Replying to @claudeai
It excels at maxing out my limits, its useless, its a total flop , one prompt and the subscription is gone, deactivate this joke
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Replying to @claudeai
No arguing about its ability. bt whats the point if one Cant Afford it?
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Replying to @claudeai
Is that why you guys watered down Fable 5?
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Replying to @claudeai
I'm building the next robotic future with this.
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Replying to @claudeai
Mythos is named that way because it’s a myth that this lousy product can do anything—I’ve had a 100% failure rate so far.
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Replying to @claudeai
And Mythos?
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Replying to @claudeai
Hey @grok What would you do with a model this cappable? And is it good from Grok latest models?
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Replying to @claudeai
Back to openai fuckers , you just crossed the line, i have shit to not buy a max plan for 5 prompts with your shitty model, you dont create software with 5 prompts
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Replying to @claudeai
far-ble or fay-ble?
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Replying to @claudeai
Can we get 50% credits in fable instead of opus. No need for opus. I have a PRO plan but rarely use it bc gpt-voice is a better interface for a dislexic.
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Replying to @claudeai
I wouldn't know, in that I still can't use the model to do any of my research. I say "yes" and immediately get shuttled back to opus. Might want to rethink those claims.
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Replying to @claudeai
I have ZERO trust in you guys at this point. Your models are great for like a week and then you nerf them into the dirt... Waiting for Astra instead
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Replying to @claudeai
Is that why you guys watered down Fable 5?
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Replying to @claudeai
It’s bc opus sucked right?
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Replying to @claudeai
I find the other models are better than fable 5 at certain tasks.
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Replying to @claudeai
OmenX
@OmenX_Official
Sep 2
With @AnthropicAI having just dropped Claude Fable 5.1 and signed a $35 billion cloud deal backed by @nvidia Markets now see a 78% chance of Anthropic hitting $2 trillion valuation by year-end, and a 46% chance of reaching $2.5 trillion. omenx.com/trade?event=EVT_PR…
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Replying to @claudeai
@LilysAI_要約して
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Replying to @claudeai
@alexalbert__ hell yea
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Replying to @claudeai
复杂任务能稳住，才更像生产力而不是聊天玩具
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Replying to @claudeai
Next level research power the future of AI in science starts here
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